Recently, with the spread of storage area networks (SAN's) which connect storage devices, computers and management computers via an exclusive line like Fiber Channel (FC), computer systems are becoming large-scaled. There has been developed a technique for efficiently managing the data of the computer system, which is increasingly swelling. For example, in Patent Citation 1, a technique is disclosed in which a first storage device is connected to one or more second storage devices (also referred to as external storage devices), the storage areas of the second storage devices are virtualized as if they were storage areas of the first storage device, and the virtualized storage areas are provided for a computer (a storage virtualization technique).
With the increase in information leakage caused by a theft of a disk or the like, secure storage and management of data are attracting growing interest. For example, in Patent Citation 2, a storage device is provided with a function of encrypting a storage area and is capable of encrypting data to be read from or written into the storage area. According to the technique of Patent Citation 2, it is possible to prevent leakage of data even in the case of being affected by a theft of a disk or the like.
Furthermore, for example, in Patent Citation 3, it is thought to construct a more secure computer system by a upper storage device which has an encryption function encrypting the data of a lower storage device which does not have an encryption function.